Email invitations sent to media displayed the number 12 casting a large shadow of a 5 with the words 'It's almost here" written above, an obvious reference to the much-anticipated new version of Apple's popular iPhone.
The event will be held at the Yerba Buena Center for the Arts in San Francisco starting at 10 a.m. PT.
Tuesday's announcement confirms months of speculation about when Apple might announce the new version of its smartphone. Sept. 12 had been mentioned on numerous technology websites and blogs as the most likely date for the announcement.
Many have also speculated the company will announce a mini version of its tablet, the iPad, at a later date in October.
Photos of purported iPhone 5 circulating
Numerous photos of purported iPhone 5 parts and handsets have appeared online.
The latest were posted last week on a Chinese technology website. They showed a handset that is longer and narrower than the current version of the iPhone. The new phone is also rumoured to have a smaller dock connector, which links up iPhone accessories.
The last version of the iPhone, the iPhone 4S, was released in October 2011.
According to U.S. sales figures released in documents filed during the recent patent trial between Apple and rival cellphone maker Samsung in California, Apple has sold 85 million iPhones in the U.S. since the device came on the market in 2007 and generated more than $50 billion US in revenue from U.S. sales.
It has sold 34 million iPads in the U.S. between 2010 and the second quarter of 2012, generating revenue of $19 billion.
Apple shares rose 1.5 per cent on Tuesday, closing at $674.97 US on the NASDAQ.
The company's market capitalization is around $630 billion US, making it the most valuable publicly traded company in the world. Much of that value is fuelled by its iPhone sales, which accounted for almost half its product sales in the third quarter of 2012.
Two other cellphone makers, Nokia and Motorola, are holding their own product launches in New York Wednesday.
Nokia, which is co-hosting its event with Microsoft, is expected to launch a new smartphone running the Windows 8 operating systems, which Microsoft hopes will rival Apple's iOS and Google's Android operating systems.
Motorola is rumoured to be launching the Droid RAZR HD, an Android-based smartphone with an edge-to-edge screen, and the Droid RAZR M.